Spent much time on Falfiles.com?
Several categories of original Belgian rifles. The so-called "G" series, imported in the 60's. Stupid expensive. Later Belgian imports by Styer, Howco, Guns South and others. Still pretty expensive. A few Australian inch pattern rifles, I think under 200, imported by Joe Poyer, also stupid expensive.
Other factory built:
Argentinian, good quality, less expensive than the Belgian ones. Some complete rifles imported before the Bush 89 import ban. Usually barrel, upper receiver, bolt, bolt carrier and lower (with firing mechanism,) all have the same SN. Some rifles in the pipeline were separated (upper receiver is the serial numbered "gun",) into upper & lower and then sold separately. Occasionally you find those, mismatched SNs but shoot just as well. Most imported by Armscorp.
Brazilian Imbel manufactured. Sold by Springfield Armory as SAR 48. After the 89 ban Springfield switched to a thumbhole stock and called them SAR4800 but still a factory built gun and can be converted back to the original config now.
Some other factory built guns imported in small quantities. Best to check on Falfiles if you run into one you think may be one of those.
Many many Imbel receivers imported and used to build complete guns on parts kits imported from Brazil (so Imbel on Imbel parts kit,) as well as Austrian Styer parts kits (STG-58's.)
Some Argentinian receivers imported and built on various kits.
In recent years German G1 kits imported and built on a variety of receivers. See Falfiles for more discussion.
Any of the above - from original G series Belgians to Imbel parts kit guns on Imbel receivers would be good.
Really, the key factor is does it run well. If you buy from a private party and it doesn't run well you're stuck getting it fixed so best to go with a high likelihood of success combination. Or get a DSA and they'll warranty the gun. In Arizona, Mark Graham, AZResponseSystems is a known FAL gunsmith but with long wait times.
Century built guns from Imbel and Argentinian receivers plus other receivers. CAI guns have a so-so reputation, some run fine, probably those built on factory receivers, others not so much.
Quite a few US receiver makers, some good, some less so. DSA is the only one still in business. Coonan, Enterprise
Hesse had a bad reputation.
Many many parts kits imported. Israel, Rhodesia, inch-pattern from the UK, Canada, Aus. Lots of variety out there.
Some US receivers were cast, some were forged. Endless debate.